Reheat scheduling for water heaters

ABSTRACT

A method for controlling reheating of a tank-style water heater having an upper heating element and a lower heating element is described. The method identifies whether the upper heating element, and optionally whether the lower heating element, or neither of the upper heating element and the lower heating element, is energized when electrical power is supplied to the water heater. The method determines whether to continue supply of electrical power to the water heater based on which of the upper heating element, or optionally the lower heating element, or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater. The method may be implemented by a controller adapted to selectively permit and deny supply of electrical power to the water heater, where the controller executes program logic for implementing the method.

TECHNICAL FIELD

The present disclosure relates to water heaters, and more particularly to scheduling of reheating cycles for water heaters.

BACKGROUND

There have been many attempts to balance the load on electrical utilities, and to distribute demand either more evenly throughout the day or into periods where the electricity has lower costs. One particular target of these efforts has been water heaters, given their significant electrical demands.

U.S. Pat. No. 6,208,806 to Newton Langford describes a domestic water heater that includes a water meter and a timer. A programmable means stores water usage and heating data to determine the time period required for heating the water in the tank, and also stores power load curve data from the power utility and matches the required heating time to an appropriate portion of a low in the power load curve. By pre-allocating the tanks into groups, a power utility can reallocate the water heater power load into low cost periods of the power load curve.

SUMMARY

In one aspect, a method for reheating a tank-style water heater comprises obtaining full reheating duration data from a volumetric tank flow for the tank, communicating the full reheating duration data to a power scheduler, and, responsive to a timed full reheat signal from the power scheduler, initiating a full reheating cycle for the tank to reheat the water in the tank to the setpoint temperature, wherein the timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time.

In one embodiment, the full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated from the volumetric tank flow. In and the power scheduler may calculate a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow.

In some embodiments, the volumetric tank flow may be one of a volumetric inflow into the tank, a volumetric outflow from the tank, and a combination of the volumetric inflow into the tank and the volumetric outflow from the tank.

In some embodiments, the power scheduler may be one of a power utility and a third party power scheduler.

In some embodiments, the method may further comprise, responsive to the volumetric tank flow exceeding a first reheat threshold, initiating a first interim reheating cycle for the tank, after the first interim reheating cycle, curtailing heating of the tank, obtaining first updated full reheating duration data according to the first interim reheating cycle and the volumetric tank flow, and communicating the first updated full reheating duration data to the power scheduler. In one such embodiment, the first updated full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated from the volumetric tank flow and the first interim reheating cycle. In another such embodiment, the first updated full reheating duration data may comprise the volumetric tank flow and first interim reheating cycle data, and the power scheduler may calculate a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow and the first interim reheating cycle data.

In some embodiments, the predetermined time may be based on load balancing by the power scheduler.

In some embodiments, the first interim heating cycle may be initiated immediately upon exceeding the first reheat threshold. In other embodiments, the first interim heating cycle may be scheduled for a time after exceeding the first reheat threshold.

In some embodiments, the method may further comprise, responsive to the volumetric tank flow exceeding a second reheat threshold that is greater than the first reheat threshold, initiating a second interim reheating cycle for the tank, after the second interim reheating cycle, again curtailing heating of the tank, obtaining second updated full reheating duration data according to the second interim reheating cycle and the volumetric tank flow, and communicating the second updated full reheating duration data to the power scheduler.

In some embodiments, the second updated full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated from the volumetric tank flow, the first interim reheating cycle and the second interim reheating cycle. In other embodiments, the second updated full reheating duration data may comprise the volumetric tank flow, the first interim reheating cycle data and the second interim reheating cycle data, and the power scheduler my calculate a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow, the first interim reheating cycle data and the second interim reheating cycle data.

In some embodiments, communicating the full reheating duration data to the power scheduler may occur daily.

In another aspect, a controller for controlling reheating of a tank-style water heater is provided. The controller is adapted to selectively activate and deactivate at least one water heater heating element and cause the at least one water heater heating element to perform heating until deactivated by the controller or terminated by at least one respective water heater limit switch. The controller is adapted to monitor volumetric tank flow for the water heater and to communicate with a power scheduler. The controller executes program logic for obtaining full reheating duration data from a volumetric tank flow for the tank, communicating the full reheating duration data to the power scheduler, and responsive to a timed full reheat signal from the power scheduler, initiating a full reheating cycle for the tank to reheat the water in the tank to the setpoint temperature. The timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time.

In one embodiment, the full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated from the volumetric tank flow. In and the power scheduler may calculate a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow.

In some embodiments, the volumetric tank flow may be one of a volumetric inflow into the tank, a volumetric outflow from the tank and a combination of the volumetric inflow into the tank and the volumetric outflow from the tank.

In some embodiments, the power scheduler may be one of a power utility and a third party power scheduler.

In some embodiments, the controller may further execute program logic for, responsive to the volumetric tank flow exceeding a first reheat threshold, initiating a first interim reheating cycle for the tank, after the first interim reheating cycle, curtailing heating of the tank, obtaining first updated full reheating duration data according to the first interim reheating cycle and the volumetric tank flow, and communicating the first updated full reheating duration data to the power scheduler.

In some embodiments, the first updated full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated from the volumetric tank flow and the first interim reheating cycle. In other embodiments, the first updated full reheating duration data may comprise the volumetric tank flow and first interim reheating cycle data, and the power scheduler may calculate a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow and the first interim reheating cycle data.

In some embodiments, the predetermined time may be based on load balancing by the power scheduler.

In some embodiments, the first interim heating cycle may be initiated immediately upon exceeding the first reheat threshold. In other embodiments, the first interim heating cycle may be scheduled for a time after exceeding the first reheat threshold.

In some embodiments, the controller may further execute program logic for, responsive to the volumetric tank flow exceeding a second reheat threshold that is greater than the first reheat threshold, initiating a second interim reheating cycle for the tank, after the second interim reheating cycle, again curtailing heating of the tank, obtaining second updated full reheating duration data according to the second interim reheating cycle and the volumetric tank flow, and communicating the second updated full reheating duration data to the power scheduler.

In some embodiments, the second updated full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated from the volumetric tank flow, the first interim reheating cycle and the second interim reheating cycle.

In some embodiments, the second updated full reheating duration data may comprise the volumetric tank flow, the first interim reheating cycle data and second interim reheating cycle data, and the power scheduler may calculate a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow, the first interim reheating cycle data and the second interim reheating cycle data.

In some embodiments, the controller may be configured to communicate the full reheating duration data to the power scheduler daily.

In another aspect, a method for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element comprises monitoring the water heater for presence or absence of an upper heating element activation signal indicating activation of the upper heating element, responsive to detecting the presence of the upper heating element activation signal, permitting supply of electrical power to the water heater, and responsive to detecting the absence of the upper heating element activation signal, denying supply of electrical power to the water heater outside of a scheduled time.

In some embodiments, the water heater has at least one intermediate heating element disposed between the upper heating element and the lower heating element.

In another aspect, a controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element is provided. The controller is adapted to selectively permit and deny supply of electrical power to the water heater and is adapted to detect an upper heating element activation signal indicating activation of the upper heating element. The controller executes program logic for monitoring the water heater for presence or absence of the upper heating element activation signal, responsive to detecting the presence of the upper heating element activation signal, permitting supply of electrical power to the water heater and, responsive to detecting the absence of the upper heating element activation signal, denying supply of electrical power to the water heater outside of a scheduled time.

In a further aspect, a method for reheating a tank-style water heater having an upper heating element and a lower heating element comprises monitoring a volumetric tank flow for the tank, responsive to the volumetric tank flow exceeding a first reheat threshold, testing the water heater for presence or absence of an upper heating element activation signal indicating activation of the upper heating element, responsive to detecting the presence of the upper heating element activation signal, initiating a first interim reheating cycle for the tank and, after the first interim reheating cycle, curtailing heating of the tank, and responsive to detecting the absence of the upper heating element activation signal, delaying the first interim reheating cycle for the tank.

In some embodiments of the method, initiating the first interim reheating cycle for the tank comprises permitting supply of electrical power to the water heater and delaying the first interim reheating cycle for the tank comprises denying supply of electrical power to the water heater outside of a scheduled time.

In yet a further aspect, a controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element is provided. The controller is adapted to control activation and deactivation of the upper heating element and the lower heating element and cause the upper heating element and the lower heating element to perform heating until deactivated by the controller or terminated by a respective limit switch. The controller is also adapted to monitor volumetric tank flow for the water heater and to detect an upper heating element activation signal indicating activation of the upper heating element. The controller executes program logic for monitoring the volumetric tank flow for the tank, responsive to the volumetric tank flow exceeding a first reheat threshold, testing the water heater for presence or absence of the upper heating element activation signal indicating activation of the upper heating element, responsive to detecting the presence of the upper heating element activation signal, initiating a first interim reheating cycle for the tank and, after the first interim reheating cycle, curtailing heating of the tank and, responsive to detecting the absence of the upper heating element activation signal, delaying the first interim reheating cycle for the tank.

In some embodiments of the controller, initiating the first interim reheating cycle for the tank comprises permitting supply of electrical power to the water heater and delaying the first interim reheating cycle for the tank comprises denying supply of electrical power to the water heater outside of a scheduled time.

In yet a further aspect, a method for reheating a tank-style water heater having an upper heating element and a lower heating element, comprises obtaining full reheating duration data from a volumetric tank flow for the tank communicating the full reheating duration data to a power scheduler and, responsive to a timed full reheat signal from the power scheduler, initiating a full reheating cycle for the tank to reheat the water in the tank to a setpoint temperature. The timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time. The method further comprises, responsive to the volumetric tank flow exceeding a first reheat threshold where an upper heating element activation signal indicating activation of the upper heating element is present, initiating a first interim reheating cycle for the tank, after the first interim reheating cycle, curtailing heating of the tank, obtaining first updated full reheating duration data according to the first interim reheating cycle and the volumetric tank flow, and communicating the first updated full reheating duration data to the power scheduler.

In another aspect, a controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element is provided. The controller is adapted to control activation and deactivation of the upper heating element and the lower heating element and cause the upper heating element and the lower heating element to perform heating until deactivated by the controller or terminated by a respective limit switch. The controller is adapted to monitor volumetric tank flow for the water heater, to detect an upper heating element activation signal indicating activation of the upper heating element, and to communicate with a power scheduler. The controller executes program logic for obtaining full reheating duration data from the volumetric tank flow for the tank, communicating the full reheating duration data to the power scheduler and, responsive to a timed full reheat signal from the power scheduler, initiating a full reheating cycle for the tank to reheat the water in the tank to a setpoint temperature. The timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time. The controller executes further program logic for, responsive to the volumetric tank flow exceeding a first reheat threshold where the upper heating element activation signal is present, initiate a first interim reheating cycle for the tank, after the first interim reheating cycle, curtailing heating of the tank, obtaining first updated full reheating duration data according to the first interim reheating cycle and the volumetric tank flow and communicating the first updated full reheating duration data to the power scheduler.

In a still further aspect, a method for reheating a tank-style water heater having an upper heating element and a lower heating element comprises obtaining full reheating duration data from a volumetric tank flow for the tank, communicating the full reheating duration data to a power scheduler and, responsive to a timed full reheat signal from the power scheduler, initiating a full reheating cycle for the tank to reheat the water in the tank to a setpoint temperature. The timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time. The method further comprises, responsive to determining an upper heating element activation signal indicating activation of the upper heating element is present, initiating a first interim reheating cycle for the tank, after the first interim reheating cycle, curtailing heating of the tank, obtaining first updated full reheating duration data according to the first interim reheating cycle and the volumetric tank flow and communicating the first updated full reheating duration data to the power scheduler.

In still yet a further aspect, a controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element is provided. The controller is adapted to control activation and deactivation of the upper heating element and the lower heating element and cause the upper heating element and the lower heating element to perform heating until deactivated by the controller or terminated by a respective limit switch. The controller is further is adapted to monitor volumetric tank flow for the water heater, to detect an upper heating element activation signal indicating activation of the upper heating element, and to communicate with a power scheduler. The controller executes program logic for obtaining full reheating duration data from a volumetric tank flow for the tank, communicating the full reheating duration data to a power scheduler and, responsive to a timed full reheat signal from the power scheduler, initiating a full reheating cycle for the tank to reheat the water in the tank to a setpoint temperature. The timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time. The controller executes further program logic for, responsive to determining the upper heating element activation signal is present, initiating a first interim reheating cycle for the tank, after the first interim reheating cycle, curtailing heating of the tank, obtaining first updated full reheating duration data according to the first interim reheating cycle and the volumetric tank flow and communicating the first updated full reheating duration data to the power scheduler.

In another aspect, a method for controlling reheating of a tank-style water heater having an upper heating element and a lower heating element, comprises identifying whether the upper heating element, the lower heating element, or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater, and determining whether to continue supply of electrical power to the water heater based on which of the upper heating element, the lower heating element or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater.

In a further aspect, a controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element is provided. The controller is adapted to selectively permit and deny supply of electrical power to the water heater, and the controller executes program logic for identifying whether the upper heating element, the lower heating element, or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater, and determining whether to continue supply of electrical power to the water heater based on which of the upper heating element, the lower heating element or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater.

In yet another aspect, a method for controlling reheating of a tank-style water heater having an upper heating element and a lower heating element, comprises identifying whether the upper heating element will be energized when electrical power is supplied to the water heater, and supplying the electrical power to the water heater only when the upper heating element will be energized thereby.

In still yet a further aspect, a controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element is adapted to selectively permit and deny supply of electrical power to the water heater and the controller executes program logic for identifying whether the upper heating element will be energized when electrical power is supplied to the water heater and supplying the electrical power to the water heater only when the upper heating element will be energized thereby.

In some implementations of the above-described embodiments, the upper heating element activation signal is a current in a circuit of the upper heating element when electrical power is supplied to the water heater. In other implementations of the above-described embodiments, the upper heating element activation signal is an electrical characteristic of the water heater when electrical power is supplied to the water heater. The electrical characteristic may be a current at an electrical input of the water heater or a resistance at an electrical input of the water heater. In some implementations of the above-described embodiments, the upper heating element activation signal is a sensor signal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings wherein:

FIG. 1 is a block diagram showing an illustrative tank-style electric water heater with a controller according to an aspect of the present disclosure;

FIG. 2 is a flowchart showing a first illustrative method for reheating water in a tank-style electric water heater;

FIG. 3 is a plot showing a function and a best fit line relating volume of water consumption (since tank was last fully reheated and then power curtailed) to load, represented both in kW hours and by reheating time;

FIG. 4 is a flow chart showing a second illustrative method for reheating water in a tank-style electric water heater;

FIG. 4A is a flow chart showing a third illustrative method for reheating water in a tank-style electric water heater FIG. 5 is a flow chart showing a fourth illustrative method for reheating water in a tank-style electric water heater;

FIG. 6 is a flowchart showing a fifth illustrative method for reheating water in a tank-style electric water heater; and

FIG. 7 is a flowchart showing a sixth illustrative method for reheating water in a tank-style electric water heater;

DETAILED DESCRIPTION

Reference is now made to FIG. 1 , which shows an illustrative tank-style electric water heater 100 coupled to a controller 120 according to an aspect of the present disclosure. The water heater 100 comprises a tank 101 and includes a lower heating element 102, a lower thermostatically controlled temperature limit switch 104, an upper heating element 106, an upper thermostatically controlled temperature limit switch 108, and an electrical junction 110. For clarity, the terms “lower” and “upper” refer to the physical position of the heating elements and temperature limit switches when the water heater 100 is upright, and not to temperature values. The electrical junction 110 is coupled in electrical communication with an electrical power supply 112, for example 220V AC, via a relay circuit 128. Electrical power to the lower heating element 102 and the upper heating element 106 from the junction 110 is governed by the temperature limit switches 104, 108. The lower temperature limit switch 104 and the upper temperature limit switch 108 are typically robust thermo-mechanical thermostats, such as adjustable mechanical “snap-disk” thermostats that physically open an electrical circuit when a set temperature is reached, although other types of thermostatically controlled temperature limit switches may be used. Other components of the water heater 100 are known to those of skill in the art, and are omitted for simplicity of illustration.

The water heater 100 has a water inlet 114 for receiving cooler water into the tank 101, for example from a municipal water supply, a water outlet 116 for releasing heated water from the tank 101, and may include a mixing valve 118 for mixing the cooler water with the heated water to achieve a more comfortable temperature.

In one typical embodiment, when both the lower temperature limit switch 104 and the upper temperature limit switch 108 are open, indicating the temperature has risen above a predetermined level (the setpoint temperature), the open temperature limit switches 104, 108 will interrupt the electrical power to the lower heating element 102 and the upper heating element 106, respectively, to prevent overheating. Where a mixing valve (e.g. mixing valve 118) is present to prevent scalding, the predetermined level may be set to 60° C. or higher to comply with World Health Organization recommendations for Legionella control. Other types of electric water heater may have a single heating element and a single temperature limit switch, or more than two heating elements and temperature limit switches (e.g. three). For example, a water heater may have at least one intermediate heating element disposed between the upper heating element and the lower heating element. In any case, when all of the temperature limit switch(es) are open, indicating that the setpoint temperature has been reached, the temperature limit switch(es) will interrupt the electrical power to the heating element(s) and the water heater will cease to draw current. Accordingly, unless interrupted by the controller 120, where the setpoint temperature is 60° C. or higher, the water heater will only cease to draw current when the temperature has reached a level sufficient to comply with WHO recommendations for Legionella control. Optionally, a safety override circuit as described in Canadian Patent Application No. 3,129,944 filed Sep. 3, 2021 may be used for Legionella control during load shifting.

The controller 120 monitors volumetric tank flow, and communicates with a power scheduler 122, which may be a power utility or a third party power scheduler, which may in turn cooperate with the power utility. In the illustrated embodiment, the controller 120 is coupled to flow meters 123 on both the water inlet 114 and the water outlet 116, although in other embodiments the controller may be coupled only to a flow meter on the water inlet or only to a flow meter on the water outlet. Thus, the volumetric tank flow may be the volumetric inflow into the tank (e.g. through water inlet 114), the volumetric outflow from the tank (e.g. through water outlet 116), or may be a combination of the volumetric inflow into the tank and the volumetric outflow from the tank. The controller 120 obtains full reheating duration data 124 from the volumetric tank flow, and can communicate the full reheating duration data 124 to the power scheduler 122. For example, the controller 120 may include a wireless communication module 125 (e.g. Wi-Fi) to communicate with a local network which is in turn coupled to the Internet so as to be able to communicate with the power scheduler 122 through the Internet.

The full reheating duration data 124 is data which enables the power scheduler 122 to determine approximately how long it will take to fully reheat the water in the tank to the setpoint temperature, and can take a number of forms. It will be appreciated that the amount of time needed to fully reheat the water in the tank to the setpoint temperature will depend on several factors, including the volumetric tank flow, the temperature of the water coming into the water inlet 114 and the energy output of the heating element(s) (e.g. heating elements 102, 106).

In some embodiments, the full reheating duration data 124 consists of an estimated or calculated duration required to fully reheat the tank to the setpoint temperature, which may be generated locally (e.g. by the controller 120). The duration may be obtained from the volumetric tank flow as well as other data, such as actual (e.g. measured) or more preferably estimated (e.g. seasonal approximation) temperature of the water coming into the water inlet 114 a reheating profile for the water heater, which may include information about the rate of energy transfer from the heating elements 102, 106. Alternatively or additionally, historical values for the amount of time needed to fully reheat after known amounts of volumetric tank flow may be used. For example, the controller 120 may have an initialization period during which the historical values are generated, and may then periodically or continuously update the historical values. The historical values may also be seasonal (e.g. different historical values for different parts of the year), or a seasonal adjustment may be applied (e.g. where historical values from December are to be used for calculations in January, an adjustment may be applied to reflect an expectation that the incoming water will be colder in January). Alternatively, the full reheating duration data 124 communicated at step 208 may comprise, or may consist solely of, the volumetric tank flow, and automated computer systems associated with the power scheduler 122 may carry out the actual calculation of the duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow. For example, the power scheduler computer systems may store a reheating profile for the water heater as well as seasonally estimated temperatures for the water entering the water inlet 114. The full reheating duration data 124 may include load requirements.

The controller 120 is also coupled to and can control the heating elements 102, 106. The controller 120 is adapted to selectively activate and deactivate the heating elements 102, 106 and cause the heating elements 102, 106 to perform heating until deactivated by the controller 120 or by the respective limit switches 104, 108. Although the controller 120 is shown as mounted on an exterior of the tank 101 for purposes of illustration, this is merely one example, and the controller 120 may be mounted elsewhere, for example on a wall, as long as it is electrically coupled to the relevant components. In a preferred embodiment, the controller 120 is not integrated directly with the internal electronics of the water heater 100. Instead, the controller is configured to selectively permit and deny supply of electrical power to the water heater 100 and thereby indirectly control the heating elements 102, 106. For example, in the illustrated embodiment the controller 120 is coupled to the electrical junction 110, although other configurations are possible. This arrangement facilitates retrofitting to existing water heaters, and reduces potential safety or warranty issues associated with alterations to internal electrical wiring of the water heater 100. It is also contemplated, however, that the controller 120 may be integrated into the electronics of the water heater 100 so as to more directly control the heating elements 102, 106. For example, the controller 120 may be integrated into a water heater 100 as supplied by an original equipment manufacturer. The power scheduler 122 can send a timed full reheat signal 126 to the controller 120 and, responsive to the timed full reheat signal 126 from the power scheduler 122, the controller 120 initiates a full reheating cycle to the setpoint temperature. The timed full reheat signal 126 times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time according to an estimated full reheating time (the estimated duration required to fully reheat the tank to the setpoint temperature) so as to take advantage of available load capacity of the power utility, availability of lower carbon electricity, or availability of lower cost electricity. For example, the predetermined time may be based on load balancing by the power scheduler 122. The timed full reheat signal 126 may be a signal to immediately begin the full reheating cycle, wherein the signal is sent at a time such that full reheating will be completed prior to the predetermined time. Or, the timed full reheat signal 126 may be a signal to begin the full reheating cycle at a later time, wherein commencement of the full reheating cycle will enable completion of the full reheating cycle before the predetermined time (i.e. the full reheat signal may contain a start time). The word “timed” in the phrase “timed full reheat signal” refers to signal causing the water heater 100 to begin a full reheating cycle at a time such that estimated full reheating time (the estimated duration required to fully reheat the tank to the setpoint temperature) will be complete before the predetermined time. Thus, by way of non-limiting example, if the predetermined time is 5:00 am and the estimated full reheating time is two hours, the timed full reheat signal 126 would be configured to cause the controller 120 to energize the water heater 100 by no later than 3:00 am. Once the water heater 100 begins a full reheating cycle, the heating element(s) 102, 106 will remain active until the water reaches the setpoint temperature, regardless of the estimated full reheating time, which may be different from the actual time required to fully reheat the water to the setpoint temperature. For example, the estimated full reheating time may not be precisely correct, or more hot water may be used during the full reheating cycle, which will increase the time required. Continuing the aforesaid non-limiting example, if the water heater 100 were to be energized at 3:00 am but actual time required to complete the full reheating cycle were longer than two hours, the controller 120 would maintain the full reheating cycle past 5:00 am until the setpoint temperature is reached and the temperature limit switches 104, 108 deactivate the heating elements 102, 106. It is expected that in most cases the estimated full reheating time will be very close to actual time required for full reheating.

The controller 120 is further able to provide for interim reheating, apart from the timed full reheat signal 126, to avoid cold-water events.

Reference is now made to FIG. 2 , which is a flow chart showing an illustrative method 200 for reheating water in a tank-style water heater. The method 200 may, for example, be administered by the controller 120, which may execute program logic for implementing the method 200. In some embodiments, the controller 120 is a programmable logic controller (PLC), although any suitable controller may be used.

At step 202, the method 200 begins with the tank (e.g. tank 101) fully heated at a setpoint temperature (e.g. 60° C. or higher to comply with WHO recommendations for Legionella control) and resets the volumetric tank flow. At step 204, the method 200 curtails heating of the tank.

At step 206, the method 200 obtains full reheating duration data (e.g. full reheating duration data 124 in FIG. 1 ) from at least a volumetric tank flow for the tank. The volumetric tank flow is monitored to obtain the full reheating duration data, which may be according to any of the methods described above, for example (other data may also be embodied in the full reheating duration data). Preferably, the method 200 communicates the full reheating duration data to a power scheduler (e.g. power scheduler 122, such as a power utility or a third party power scheduler) at predetermined intervals, for example once per hour, or once per day at a suitable time to enable scheduling of a full reheating cycle for all of the water heaters managed by the power scheduler. Thus, in the illustrated embodiment the method 200 proceeds from step 206 to step 208 to check whether it is time to communicate the full reheating duration data to a power scheduler. Where it is time to communicate the full reheating duration data (“yes” at step 208), the method proceeds to step 210 and communicates the full reheating duration data, and then to step 212. If it is not yet time to communicate the full reheating duration data (“no” at step 208), the method bypasses step 210 and proceeds directly to step 212.

At step 212, the method 200 checks for a timed full reheat signal (e.g. timed full reheat signal 126) from the power scheduler. Responsive to a timed full reheat signal from the power scheduler (“yes” at step 212), the method 200 proceeds to step 214 and initiates a full reheating cycle for the tank to reheat the water in the tank to the setpoint temperature. Thus, the controller 120 may control heating elements 102, 106 and cause them to begin heating until terminated by the respective limit switches 104, 108. As noted above, the timed full reheat signal times initiation of the full reheating cycle to complete the full reheating cycle prior to a predetermined time. After step 214, the method 200 returns to step 202. Where a timed full reheat signal is not received from the power scheduler (“no” at step 212), the method proceeds to step 216.

At step 216, the method 200 tests whether the volumetric tank flow has exceeded a first reheat threshold, i.e. whether the volumetric tank flow exceeds a first predetermined volume of water. The first predetermined volume of water may be calculated based on a volume of hot water use that would begin to materially degrade the temperature of the water emerging from the water outlet 116 or mixing valve 118, or may be a predefined value wherein the remaining capacity of the tank 101 would be below a minimum level. For example, if the tank (e.g. tank 101) has a capacity of 280 litres, the first predetermined volume of water may be 185 litres, or about 66% of the capacity of the tank. This is merely an illustrative example, and is not limiting. The reheat threshold(s) will be determined by a number of factors and can change over time. Relevant factors may include, but are not limited to tank capacity, number of residents, historic water use levels, among others.

Responsive to the volumetric tank flow failing to exceed the first reheat threshold (“no” at step 216), the method 200 returns to step 206. Thus, as long as no timed full reheat signal is received at step 212 and the threshold is not exceeded at step 216, the method 200 will continue to cycle through obtaining full reheating duration data from the volumetric tank flow at step 206 and, at the appropriate time as determined at step 208, communicating the full reheating duration data to the power scheduler at step 210.

Responsive to the volumetric tank flow exceeding the first reheat threshold (“yes” at step 216), the method 200 proceeds to step 218. At step 218, the method 200 initiates a first interim reheating cycle for the tank. In some embodiments, the first interim heating cycle may be initiated immediately upon exceeding the first reheat threshold; in other embodiments the first interim heating cycle may be scheduled for a later time after exceeding the first reheat threshold; the later time may take into account load balancing, electricity cost and/or carbon footprint, for example. Scheduling of the first interim reheating cycle may be dependent on an amount by which the first reheat threshold is exceeded (equivalently the first reheat threshold may comprise a deferred reheating subthreshold and a higher immediate reheating subthreshold). For example, if the tank (e.g. tank 101) has a capacity of 280 litres and the first reheat threshold is 140 litres, the first interim heating cycle may be scheduled for some time within the next three hours (i.e. deferred reheating subthreshold is 140 litres), but if the first reheat threshold is exceeded by more than 40 litres then the first interim heating cycle may begin immediately (i.e. a 180 litre immediate reheating subthreshold). In this example, the duration of the first interim reheating cycle may be approximately thirty minutes. These are merely illustrative, non-limiting examples.

Preferably, the first interim reheating cycle does not fully reheat the tank to the setpoint temperature, but rather the heating element(s) (e.g. heating elements 102, 106) will be active for a predetermined period of time and will be deactivated before the temperature limit switch(es) (e.g. temperature limit switches 104, 108) engage.

After step 218, the method 200 proceeds to step 220, wherein the reheat threshold value(s) are updated. The first reheat threshold may be updated to a second reheat threshold. For example, if the tank has a capacity of 280 litres and the first reheat threshold is 185 litres, the second reheat threshold may be 220 litres. Again, these are merely non-limiting illustrative examples. Updating the first reheat threshold to the second reheat threshold may be by way of a stored value, or by indexing from a predefined first reheat threshold to a predefined second reheat threshold, among other techniques. Similarly, the first interim reheating cycle may be updated to a second interim reheating cycle, which may be longer than the first interim reheating cycle. Continuing the non-limiting illustrative example, if the tank has a capacity of 280 litres and the first reheat threshold is 185 litres, the duration of the first interim reheating cycle is approximately thirty minutes and the second reheat threshold is 220 litres, the second interim reheating cycle may have a duration of approximately sixty minutes. Examples of techniques for updating the first interim reheating cycle to the second interim reheating cycle include updating a stored value, and indexing from a predefined first duration to a predefined second duration, among others.

After the first interim reheating cycle initiated at step 218 and updating the reheat threshold(s) at step 220, the method 200 returns to step 204 and again curtails heating of the tank after first predetermined time, before the temperature limit switches (e.g. temperature limit switches 104, 106) engage. The method 200 then proceeds again to step 206, obtaining first updated full reheating duration data, which reflects the first interim reheating cycle and the volumetric tank flow. The first updated full reheating duration data is then communicated to the power scheduler at a second iteration of step 208.

In one embodiment, on the second iteration of step 206 the first updated full reheating duration data is a duration required to fully reheat the tank to the setpoint temperature, which is calculated from the volumetric tank flow and the first interim reheating cycle. The calculation may be similar to that used for the full reheating duration data on the first iteration of step 206, but also taking into account the heat added by the first interim reheating cycle. In this embodiment, the calculation may be carried out by the controller 120. In another embodiment, the first updated full reheating duration data comprises the volumetric tank flow as well as first interim reheating cycle data, and the power scheduler 122 calculates a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow and the first interim reheating cycle data. The first interim reheating cycle data may be any data used by the power scheduler to enable the calculation. For example, the first interim reheating cycle data may be the duration of the first interim reheating cycle, or the time of commencement or completion of the first interim reheating cycle, or merely the fact that the first interim reheating cycle has occurred (if the power schedule has a sufficient profile of the water heater 100).

After the second iteration of step 208, the method 200 proceeds once more to step 212 and, if no timed full reheat signal is received from the power scheduler (“no” at step 212), the method 200 proceeds again to step 216. Where the first reheat threshold was updated to a second reheat threshold at step 220 as described above, step 216 will test whether the volumetric tank flow exceeds the second reheat threshold. Responsive to the volumetric tank flow exceeding the second reheat threshold (“yes” at step 216), the method 200 proceeds to step 218 and initiates a second interim reheating cycle for the tank, then to step 220 to update the reheat threshold value(s), and then returns to step 204 so that after the second interim reheating cycle, heating of the tank is again curtailed. Preferably, the second interim reheating cycle does not fully reheat the tank to the setpoint temperature, but rather the heating element(s) (e.g. heating elements 102, 106) will be active for a predetermined period of time and will be deactivated before the temperature limit switches (e.g. temperature limit switches 104, 108) engage.

From step 204 the method 200 again proceeds to step 206, where the method 200 obtains second updated full reheating duration data according to the second interim reheating cycle and the volumetric tank flow. At the appropriate time as determined at step 208, the method 200 may communicate the second updated full reheating duration data to the power scheduler at step 210. The second updated full reheating duration data may be a duration required to fully reheat the tank to the setpoint temperature calculated (e.g. by the controller 120) from the volumetric tank flow, the first interim reheating cycle and the second interim reheating cycle. The second updated full reheating duration data may comprise the volumetric tank flow, the first interim reheating cycle data and second interim reheating cycle data (e.g. the duration of the second interim reheating cycle, time of commencement or completion of the second interim reheating cycle, or merely the occurrence of the second interim reheating). In this latter case, the power scheduler calculates a duration required to fully reheat the tank to the setpoint temperature from the volumetric tank flow, the first interim reheating cycle data and the second interim reheating cycle data.

In one embodiment, the method 200 may continue to iterate until a timed full reheat signal is received from the power scheduler, with interim reheating cycles performed as required according to corresponding thresholds. In other embodiments, after a certain number of interim reheating cycles, the method 200 may, if the volumetric tank flow exceeds a further threshold, initiate a full reheating cycle for the tank to reheat the water in the tank to the setpoint temperature even in the absence of a timed full reheat signal from the power scheduler. For example, if the tank has a capacity of 280 litres, the first reheat threshold is 185 litres and the second reheat threshold is 220 litres, a third reheat threshold may be set at 260 litres, and if the volumetric tank flow exceeds this third threshold, a full reheating cycle may be initiated. Stated another way, in such an embodiment the third interim reheating cycle may be a full reheating cycle.

If a subsequent threshold is exceeded before completion of a prior interim reheating cycle (e.g. if the second reheat threshold is exceeded before the first interim reheat cycle is completed), a subsequent interim reheating cycle may be added to the prior interim reheating cycle (e.g. the first interim reheating cycle may be extended by the duration of the second interim reheating cycle).

Preferably, the reheat thresholds and scheduling of interim reheat cycles are dynamically adjustable based on water usage patterns and/or rate structure and/or carbon footprint and/or load distribution, among other factors. For example, if water usage is consistently higher than expected, the reheat threshold(s) may be lowered.

Of note, the method 200 is able to estimate the duration required to fully reheat the tank without any information about measured temperature within the tank (only the setpoint temperature) and without any information about measured temperature of water entering the water inlet (historical data being used). While actual temperature measurements may be incorporated, they need not be, and it is preferable to avoid actual temperature measurements in order to avoid the need for additional sensors and to simplify the system.

Reference is now made again to FIG. 1 . Within the tank 101, the cooler water from the water inlet 114 tends to sink, while the warmer (heated) water tends to rise, such that there is a thermal gradient band 130 between the cooler water at the bottom and the warmer (heated) water at the top of the tank 101. For this reason, the water outlet 116 typically draws water from above the ¾ point of the tank 101, where the water will be warmest. When the tank 101 is fully reheated, thermal gradient band 130 will be narrow, and will be located at the bottom of the tank. As warmer water is drawn from the water outlet 116 and replaced by cooler water from the water inlet 114, thermal gradient band 130 will rise and also expand as the cooler and warmer water mix. After a certain volume of the warmer water has been consumed and replaced by the cooler water, thermal gradient band 130 will rise and expand to the point where the temperature of the water drawn from the water outlet 116 is insufficient for user comfort. While this could be obviated by a full reheating cycle, depending on the timing this may be economically inefficient and/or environmentally inefficient, and the use of the interim reheating cycles can maintain the temperature at a comfortable level while deferring a substantial amount of the reheating load.

The following provides an illustrative, non-limiting example of the method 200 where the full reheating duration data is the duration required to fully reheat the tank to the setpoint temperature, calculated from the volumetric tank flow (measured as outflow from the water outlet 116) by the controller 120. In this example, the tank 101 of the water heater 100 has a capacity of 280 litres and a setpoint temperature of 60° C., and water enters the water inlet 114 at a temperature of between 7° C. and 8° C. (winter). The first reheat threshold is set to include a deferred reheating subthreshold of 140 litres (about 50% of capacity) and an immediate reheating subthreshold of 180 litres (about 65% of capacity). The second reheat threshold is set to 220 litres (about 78% of capacity). A third reheat threshold is set at 260 litres (about 93% of capacity).

When the tank 101 is fully heated, water may enter the water outlet 116 at 60° C. and emerge from the mixing valve 118 at about 50° C. After the volumetric tank flow reaches 65 litres (about 23% of capacity) the temperature at the water outlet 116 will be about 55° C. and will still emerge from the mixing valve 118 at about 50° C. At this point, the duration required to fully reheat the tank to the setpoint temperature is about sixty minutes.

If the volumetric tank flow (which approximates consumption) is less than the deferred reheating subthreshold of 140 litres (about 50% of capacity) before a set time (e.g. 11 pm), the controller 120 estimates the load required, that is, the duration required to fully reheat the tank to the setpoint temperature, which is communicated to the power scheduler 122 as the full reheating duration data 124. The power scheduler 122 then schedules a full reheating cycle for overnight, and sends a timed full reheat signal 126 to the controller 120. By providing the duration required to fully reheat the tank to the setpoint temperature to the power scheduler in advance, the full reheating cycle can be scheduled appropriately for capacity management purposes.

If the volumetric tank flow exceeds the deferred reheating subthreshold of 140 litres (about 50% of capacity), the controller 120 schedules a first interim reheating cycle (e.g. 30 minutes) as a “top-up” reheating at some point in the near future, e.g. within the next three hours, with the balance of re-heating expected to be scheduled for overnight. The first interim reheating cycle will be scheduled to minimize consumer cost and for utility load management, and the controller 120 may communicate with the power scheduler 122 to obtain load management information and/or scheduling information for this purpose, or the same may be stored locally on the controller 120 and updated from time to time. If the volumetric tank flow exceeds the immediate reheating subthreshold of 180 litres (about 65% of capacity), the controller 120 begins the first interim reheating cycle immediately. At this point, the duration required to fully reheat the tank to the setpoint temperature is about one hundred and fifty minutes (2.5 hours), and a first interim reheating cycle of 30 minutes can increase the available hot water by 80 to 100 litres, while still deferring most reheating to more efficient time periods.

If the volumetric tank flow exceeds the second reheat threshold of 220 litres (about 78% of capacity), the controller 120 will immediately initiate the second interim reheating cycle (e.g. sixty minutes). Note that when the volumetric tank flow exceeds the second reheat threshold, it will have already exceeded the first reheat threshold and the first reheating cycle will have at least started. If the first interim reheating cycle is not yet complete when the second reheat threshold is exceeded, the additional duration of the second interim reheating cycle is added to the first interim reheating cycle.

Where the first interim reheating cycle is triggered, or both the first interim reheating cycle and the second interim reheating cycle are triggered, at the set time, the controller 120 estimates the load required, that is, the duration required to fully reheat the tank to the setpoint temperature, taking into account the updated volumetric tank flow as well as the impact of the interim reheating cycle(s). This estimated duration is communicated to the power scheduler as the full reheating duration data.

If the volumetric tank flow exceeds the third threshold 260 litres (about 93% of capacity), a full reheating cycle is initiated (the third interim reheating cycle may be a full reheating cycle).

Although references have been made to the volumetric tank flow as a percentage of capacity, it will be understood that water leaving the tank 101 through the water outlet 116 is replaced by water entering the tank 101 through the water inlet 114.

The interim reheating thresholds and the durations of the interim reheating cycles will vary seasonally. FIG. 3 is a plot showing a function and a best fit line relating volume of hot water consumption (since tank was last fully reheated and then power curtailed) to load, represented both in kW hours and by reheating time. The plot shown in FIG. 3 is for winter; the volume versus load curve varies by season (due to changes in water temperature at the water inlet) and by water heater manufacturer. The controller 120 may be programmed with suitable information to calculate or otherwise obtain the estimated duration required to fully reheat the tank to the setpoint temperature based on the volumetric tank flow representing the volume of hot water consumption, or a similar process may be undertaken at the power scheduler 122 based on the volumetric tank flow provided by the controller 120. In a situation in which heating of the tanks of two million water heaters is to be completed by 5:30 am, without advance load information, a power scheduler must assume that a full reheating cycle (of three hour duration) is required and reheating of the last water heater therefore must commence by 2:30 am. However, with the load forecasting made possible by knowing the estimated duration required to fully reheat each tank to the setpoint temperature, a substantial number of the water heaters can be scheduled to start as late as 4:30 am or even later, depending on need and load distribution objectives. This is merely an illustrative, non-limiting example.

Referring again to FIG. 1 , as noted above, when both the lower temperature limit switch 104 and the upper temperature limit switch 108 are open, indicating the temperature has risen above a predetermined level (the setpoint temperature), the open temperature limit switches 104, 108 will interrupt the electrical power to the lower heating element 102 and the upper heating element 106, respectively. In some embodiments, the upper temperature limit switch 108 can be leveraged to provide further control over the reheating process, or to provide an alternate means of control.

A typical tank style water heater (of which the water heater 100 shown in FIG. 1 is representative) will fill from the bottom via the water inlet 114, while the water outlet 116 typically draws water from the top of the tank 101, where the water will be warmest. With a conventional water heater (absent any modification according to the present disclosure) during a typical day the lower heating element 102 is activated frequently as heated water is consumed. As noted above, the cooler water from the water inlet 114 enters the bottom of the tank and stays below warmer water. When the tank is fully reheated and cooler water enters at the bottom, the mixing of warmer and cooler water stays in a limited section causing a thermal gradient band 130 between the cooler water at the bottom and the warmer (heated) water at the top of the tank 101. As such, for most water heaters, almost all reheating is done by the lower heating element 102 and the upper heating element 106 is activated only during a period of high usage where the temperature in the upper portion of the tank 101 degrades below the setpoint of the upper temperature limit switch 108. Within the control circuitry of the water heater 100, the upper temperature limit switch 108 has priority: if both temperature limit switches are closed, only the upper heating element 106 is activated; the lower heating element 102 is activated only if the lower temperature limit switch 104 is closed and the upper temperature limit switch 108 is open. Thus, if the upper temperature limit switch 108 closes because the surrounding water temperature falls below its setpoint, the upper heating element 106 is activated and remains activated (energized) until the setpoint temperature is reached, with the lower heating element 102 remaining deactivated despite the lower temperature limit switch 108 also being closed. Once the setpoint temperature is reached for the water in the upper portion of the tank 101 and the upper temperature limit switch 108 opens, heating continues with the lower heating element 102. Note that where the temperature limit switches 104, 108 are thermomechanical thermostat devices, the temperature needs to drop several degrees below the setpoint in order to trigger reheating.

The fact that the upper temperature limit switch 108 has priority can be utilized to provide additional or alternate control over reheating. Reference is now made to FIG. 4 , which is a flow chart showing a method 400 for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element. At step 402, the method 400 identifies whether the upper heating element 106, the lower heating element 102, or neither the upper heating element 106 nor the lower heating element 102 is energized when electrical power is supplied to the water heater 100. At step 404, the method 400 determines whether to continue supply of electrical power to the water heater 100 based on whether the upper heating element 106, the lower heating element 102, or neither of them, is energized when electrical power is supplied to the water heater 100. Typically, where the upper heating element 106 is energized when electrical power is supplied to the water heater 100, the method 400 will continue supply of electrical power to the water heater 100, because this indicates that the water in the upper portion of the tank 101 has fallen below the setpoint, whereas if the lower heating element 102 is energized or neither the upper heating element 106 nor the lower heating element 102 is energized when electrical power is supplied to the water heater 100, the method 400 will curtail supply of electrical power to the water heater. Supply of electrical power can be curtailed without adversely affecting performance of the water heater 100 because non-activation of the upper heating element 106 indicates that the temperature of the water in the upper portion of the tank 101, from which water is withdrawn via the water outlet 116, remains above (or at least close to) the setpoint.

FIG. 4A shows another method 400A for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element. At step 402A, the method 400A identifies whether the upper heating element will be energized when electrical power is supplied to the water heater. If the upper heating element will be energized when electrical power is supplied to the water heater (“yes” at step 402A), the method 400A proceeds to step 404A and supplies electrical power to the water heater. If the upper heating element will not be energized when electrical power is supplied to the water heater (“no” at step 402A) the method 400A returns to step 402A and continues to check. Thus, according to the method 400A, supply of electrical power to the water heater only occurs when the upper heating element will be energized thereby.

The methods 400 and 400A may be implemented, for example, by a suitably modified embodiment of the controller 120 shown in FIG. 1 .

In one embodiment, the methods 400 and 400A may be implemented by interrupting and then restoring supply of electrical power to the water heater 100, in particular to the lower heating element 102 and the upper heating element 106 via the electrical junction 110. In a particular non-limiting embodiment, the controller 120 may be configured to selectively permit and deny supply of electrical power to the water heater 100 and thereby indirectly control the heating elements 102, 106. For example, in the illustrated embodiment the controller 120 is coupled to the electrical junction 110 to achieve this end; the controller may also be coupled to the relay circuit 128. In other embodiments, sensor configurations which avoid the need to supply electrical power to the water heater 100 through the electrical junction 110 may be used. Such a sensor arrangement may provide an upper heating element activation signal indicating activation of the upper heating element without supplying electrical power to the water heater 100 through the electrical junction 110. As another non-limiting alternative, solid state relays may be used to provide a lower current for testing cycles. Any suitable direct or indirect method of monitoring when the upper heating element 106 would be activated may be used.

Determining whether to supply (or continue to supply) electrical power to the water heater 100 based on whether or not the upper heating element 106 is energized when electrical power is supplied to the water heater 100 may be implemented in conjunction with a scheduled reheating time. The scheduled reheating time may be a variable time determined using volumetric tank flow as described above, such that the scheduled reheating time will vary based on the full reheating duration data, or may be a fixed time, for example based on lower utility rates or lower carbon footprint, typically overnight (e.g. 3:00 a.m. to 5:00 a.m.).

Reference is now made to FIG. 5 , which shows an illustrative method 500 for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element.

At step 502, the method 500 checks whether the current time is within a scheduled time (which may be, for example, a predefined time or a time determined from full reheating duration data). If the current time is outside of the scheduled time (“no” at step 502), the method 500 proceeds to step 504. At step 504, the method 500 monitors the water heater for presence or absence of an upper heating element activation signal indicating activation of the upper heating element. However, if the current time is within the scheduled time (“yes” at step 502), the method 500 proceeds to step 506A and permits supply of electrical power to the water heater and then returns to step 502. As long as the current time is within the scheduled time (“yes” at step 502), the method 500 will continue supply of electrical power to the water heater. Outside of the scheduled time, however (“no” at step 502), supply of electrical power to the water heater is governed by the presence or absence of the upper heating element activation signal.

The upper heating element activation signal may take a variety of forms. In some embodiments, the upper heating element activation signal may be a sensor signal. For example, a CT clamp sensor may be used to detect the presence or absence of current in the circuitry associated with the upper heating element 106. Optionally, a CT clamp sensor may also be used to detect the presence or absence of current in the circuitry associated with the lower heating element 102 (or the circuit associated with an intermediate heating element). The CT clamp sensor(s) may be coupled to the controller 120. A CT clamp sensor on the circuit for the upper heating element 106 alone can provide a direct upper heating element activation signal—if the upper heating element 106 is energized, electrical power may continue to be supplied. A CT clamp on the circuit for the lower heating element 102 in combination with a current sensor for the water heater 100 as a whole can provide an indirect upper heating element activation signal—if the water heater 100 is drawing a current and the circuit for the lower heating element 102 is not drawing a current, it can be inferred that the upper heating element 106 is drawing the current so electrical power may continue to be supplied. Where the circuits for the upper heating element 106 and the lower heating element 102 each have a respective CT clamp and neither circuit draws a current when electrical power is supplied to the water heater 100, then supply of electrical power may be curtailed. Thus, the upper heating element activation signal may be a sensor signal from one or more sensors, for example but not limited to CT clamp sensor(s), or other sensor(s) that could be coupled to circuitry associated with the upper heating element 106 and/or the lower heating element 102 and configured to send a signal to identify which circuit was (or would be) energized. In other embodiments, the upper heating element activation signal may be an electrical characteristic of the water heater when electrical power is supplied to the water heater. For example, there is often a slight difference in the electrical resistance between any two heating elements, and the current at the electrical input to the water heater may thus indicate which heating element (if any) is activated when electrical power is supplied to the water heater. Similarly, resistance at the electrical input to the water heater may also indicate which heating element (if any) is activated when electrical power is supplied to the water heater. Thus, the electrical characteristic used as an upper heating element activation signal may be the current at the electrical input of the water heater or the resistance at the electrical input of the water heater, or a combination thereof.

At step 506B, responsive to detecting the presence of the upper heating element activation signal (“yes” at step 504), the method 500 permits (e.g. continues to permit) supply of electrical power to the water heater until the upper heating element activation signal is absent. Absence of the upper heating element activation signal indicates that the water in the upper portion of the tank has sufficiently reheated to open the upper temperature limit switch 108. Thus, as shown in FIG. 5 , as long as the upper heating element activation signal is present, the method 500 cycles through steps 504 and 506B, and once the upper heating element activation signal is absent the method 500 diverts from step 504 to step 508. At step 508, responsive to detecting the absence of the upper heating element activation signal (“no” at step 504) either initially or after a cycle including step 506B, the method 500 denies supply of electrical power to the water heater and then returns to step 502.

The following is a non-limiting illustrative example of an implementation of the method 500 shown in FIG. 5 , with reference also to FIG. 1 . The controller 120 will permit supply of electrical power to the water heater 100 via the electrical junction 110 within the scheduled time so as to permit full reheating when scheduled (steps 502 and 506A). Outside of the scheduled time, the controller 120 will by default deny supply of electrical power to the water heater 100 via the electrical junction 110 outside of the scheduled time, except that the controller will intermittently permit supply of electrical power to the water heater 100 and determine whether or not the upper heating element 106 is energized by detecting the presence or absence of the upper heating element activation signal (step 504). Supply of electrical power may be permitted at timed intervals, or at intervals based on the volume of water consumed since the previous supply of electrical power. The intervals at which the controller 120 permits supply of electrical power to the water heater 100 may depend on a number of factors, including the size and thermal characteristics of the tank 101, the capacity of the upper heating element 106, the temperature of water entering the water inlet 114, the month or season (which may serve as a proxy for water temperature), as well as other factors, and may be fixed intervals or variable intervals. If the controller 120 determines that the upper heating element 106 is not energized (“no” at step 504), this is because the upper temperature limit switch 108 is open, which indicates that the temperature of the water in the upper portion of the tank 101 remains above (or at least close to) the setpoint. The controller 120 then discontinues supply of electrical power to the water heater 100 (step 508) and no reheating will occur by either the upper heating element 106 or the lower heating element 102. If the controller 120 determines that the upper heating element 106 is energized (“yes” at step 504), this means that the upper temperature limit switch 108 is closed, indicating that the temperature of the water in the upper portion of the tank 101 has fallen below the setpoint. The controller 120 then permits continued supply of electrical power to the water heater 100, such that the upper heating element 106 remains energized. This will rapidly reheat the (already relatively warm) water in the upper portion of the tank 101 which feeds the water outlet 116, while deferring reheating of the colder water in the lower portion of the tank 101 until the scheduled time. By way of a non-limiting illustrative example, in a water heater 100 with a 60 gallon (227.125 litre) tank 101 that begins fully heated, approximately 50% of the volume can be consumed before the temperature in the upper portion of the tank 101 falls to the point where the upper temperature limit switch 108 closes. Leaving the upper heating element 106 energized for about 20 minutes will add approximately 100 litres of additional capacity (water in the upper portion of the tank 101 at a suitable temperature); this “top up” reheating can be repeated a few times (optionally with a slightly increased duration each time) to maintain availability of hot water while deferring full reheating until the scheduled time (typically overnight). Once the controller 120 determines that the upper heating element 106 is no longer energized (because the temperature of the water in the upper portion of the tank 101 has risen sufficiently to open the upper temperature limit switch 108), supply of electrical power to the water heater 100 is again denied (step 508).

Controlling reheating based on whether or not the upper heating element 106 is energized when electrical power is supplied to the water heater 100 may be implemented as an alternative to, or in conjunction with, the use of volumetric measurement to control interim reheating. Where used as an alternative, the full reheating duration data may be used to determine a scheduled reheating time, while the determination of whether to perform an interim reheating cycle is made based on whether or not the upper heating element 106 is energized when electrical power is supplied to the water heater 100 rather than based on volumetric measurement. When used in conjunction with volumetric measurement, an interim reheat cycle will be initiated only where the volumetric measurement indicates that an interim reheating cycle is appropriate and the upper heating element 106 is energized when electrical power is supplied to the water heater. In one embodiment, even if the volumetric measurement indicates that an interim reheating cycle is appropriate, the controller 120 will first test whether the upper heating element 106 is energized when electrical power is supplied to the water heater 100. If not, reheating is delayed to prevent the lower heating element 102 from being energized first. Although this is unlikely, during summer months where the water entering through the water inlet 114 is warmer, it is possible that the volumetric measurement may indicate that an interim reheating cycle is appropriate while the upper temperature limit switch 108 remains open.

Reference is now made to FIG. 6 , which shows an illustrative method 600 for reheating a tank-style water heater having at least an upper heating element and a lower heating element in which full reheating duration data may be used to determine a scheduled reheating time, while the determination of whether to perform an interim reheating cycle is made solely based on whether or not the upper heating element 106 is energized when electrical power is supplied to the water heater 100. The method 600 may, for example, be administered by the controller 120, which may execute program logic for implementing the method 600.

The method 600 shown in FIG. 6 is similar to the method 200 shown in FIG. 2 , with like reference numerals denoting like features except with the prefix “6” instead of “2”, and as such details described above in the context of FIG. 2 are not repeated here. The method 600 shown in FIG. 6 differs from the method 200 shown in FIG. 2 in that instead of testing whether the volumetric tank flow has exceeded a reheat threshold at step 216, at step 616A the method 600 tests whether an upper heating element activation signal indicating activation of the upper heating element is present. For example, the controller 120 may permit the temporary supply of electrical power to test whether the upper heating element activation signal is present when electrical power is supplied to the water heater 100. Responsive to determining that the upper heating element activation is not present (“no” at step 616A), the method 600 returns to step 606. Thus, as long as no timed full reheat signal is received at step 612 and the upper heating element activation signal is not present at step 616A, the method 600 will continue to cycle through obtaining full reheating duration data from the volumetric tank flow at step 606 and, at the appropriate time as determined at step 608, communicating the full reheating duration data to the power scheduler at step 610.

Responsive to determining that the upper heating element activation is present (“yes” at step 616A), the method 600 proceeds to step 618 to initiate an interim reheating cycle for the tank, and then to step 620 and back to step 604 where heating is curtailed.

Reference is now made to FIG. 7 , which shows an illustrative method 700 for reheating a tank-style water heater having at least an upper heating element and a lower heating element in which full reheating duration data may be used to determine a scheduled reheating time, and where the determination of whether to perform an interim reheating cycle is made based on a combination of volumetric tank flow and whether or not the upper heating element 106 is energized when electrical power is supplied to the water heater 100. The method 700 may, for example, be administered by the controller 120, which may execute program logic for implementing the method 700.

The method 700 shown in FIG. 7 is similar to the method 200 shown in FIG. 2 , with like reference numerals denoting like features except with the prefix “7” instead of “2”, and as such details described above in the context of FIG. 2 are not repeated here. The method 700 shown in FIG. 7 differs from the method 200 shown in FIG. 2 in that in addition to testing whether the volumetric tank flow has exceeded a reheat threshold at step 716, at step 716A the method 700 tests whether an upper heating element activation signal indicating activation of the upper heating element is present. Thus, if the method 700 determines at step 716 that the volumetric tank flow has exceeded the reheat threshold (“yes” at step 716), the method 700 proceeds to step 716A to test whether the upper heating element activation signal is present or absent. Responsive to determining that the upper heating element activation is present (“yes” at step 716A), the method 700 proceeds to step 718 to initiate an interim reheating cycle for the tank, and then to step 720 and back to step 704 where heating is curtailed. Initiating the interim reheating cycle may comprise permitting (e.g. continuing to permit) supply of electrical power to the water heater. However, responsive to determining either that the volumetric tank flow has not exceeded the reheat threshold (“no” at step 716) or that the upper heating element activation signal is absent (“no” at step 716A), the method 700 returns to step 706. Accordingly, the interim reheating cycle is initiated responsive to the volumetric tank flow exceeding a reheat threshold where the upper heating element activation signal indicating activation of the upper heating element is present, and an interim reheat cycle is only initiated where the volumetric tank flow has exceeded the reheat threshold (“yes” at step 716) and the upper heating element activation is present (“yes” at step 716A); both conditions must be satisfied. Even if the volumetric tank flow has exceeded the reheat threshold (“yes” at step 716), responsive to detecting the absence of the upper heating element activation signal (“no” at step 716A), the method 700 delays the interim reheating cycle. Delaying the interim reheating cycle may comprise denying supply of electrical power to the water heater outside of a scheduled time. Accordingly, as long as no timed full reheat signal is received at step 712 and either the volumetric tank flow has not exceeded the reheat threshold (“no” at step 716) or the upper heating element activation signal is absent (“no” at step 716A), the method 700 will continue to cycle through obtaining full reheating duration data from the volumetric tank flow at step 706 and, at the appropriate time as determined at step 708, communicating the full reheating duration data to the power scheduler at step 710. Steps 716 and 716A may be performed in reverse order.

The use of volumetric tank flow to determine a scheduled reheating time requires installing at least one water volume meter with each tank, which is a straightforward process when a new water heater is installed, and the use of an upper heating element activation signal to govern interim reheating can be integrated into this approach. Thus, a combination of volumetric tank data for scheduling full reheating with use of an upper heating element activation signal to govern interim reheating is well suited to new installations (including replacements).

For existing water heaters, the use of an upper heating element activation signal to govern interim reheating can still be employed without the need to install water meter(s), with full reheating being scheduled for fixed times rather than times determined from volumetric tank flow.

In one embodiment, a second electrical box can be retrofit onto an existing water heater with a short visit by an electrician and no plumber is required. This system does not provide an estimate of reheating power required, but can limit daytime reheating to the upper heating element and permit scheduling of full reheating so as to defer the bulk of reheating until desired periods (e.g. overnight periods). In this embodiment, in addition to the high voltage electrical relay, a second, low voltage controller is coupled to the electrical relay and configured to control supply of electrical power to the water heater through the electrical relay. In other embodiments, the electrical relay and the controller may be integrated.

As can be seen from the above description, the reheating control technology described herein represent significantly more than merely using categories to organize, store and transmit information and organizing information through mathematical correlations. The reheating control technology is in fact an improvement to the technology of tank-style electric water heaters, as they provide improved control over the timing of electrical power supply for reheating while supporting continuous availability of hot water. This facilitates improved control over peak load management and load distribution. Moreover, the reheating control technology is applied by using a particular machine, namely a tank-style electric water heater. As such, the reheating control technology is confined to tank-style electric water heater applications. Certain currently preferred embodiments have been described by way of example. It will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims. 

What is claimed is:
 1. A controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element, wherein: the controller is adapted to selectively permit and deny supply of electrical power to the water heater; the controller is adapted to detect an upper heating element activation signal indicating activation of the upper heating element; and the controller executes program logic for: monitoring the water heater for presence or absence of the upper heating element activation signal; responsive to detecting the presence of the upper heating element activation signal, permitting the supply of electrical power to the water heater; and responsive to detecting the absence of the upper heating element activation signal, denying the supply of electrical power to the water heater outside of a scheduled time.
 2. The controller of claim 1, wherein the upper heating element activation signal is a current in a circuit of the upper heating element when electrical power is supplied to the water heater.
 3. The controller of claim 1, wherein the upper heating element activation signal is an electrical characteristic of the water heater when electrical power is supplied to the water heater.
 4. The controller of claim 3, wherein the electrical characteristic is a current at an electrical input of the water heater.
 5. The controller of claim 3, wherein the electrical characteristic is a resistance at an electrical input of the water heater.
 6. The controller of claim 1, wherein the upper heating element activation signal is a sensor signal.
 7. A controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element, wherein: the controller is adapted to selectively permit and deny supply of electrical power to the water heater; and the controller executes program logic for: identifying whether the upper heating element, the lower heating element, or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater; and determining whether to continue supply of electrical power to the water heater based on which of the upper heating element, the lower heating element or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater.
 8. The controller of claim 7, wherein the controller is adapted to detect an upper heating element activation signal indicating activation of the upper heating element.
 9. The controller of claim 8, wherein the upper heating element activation signal is a current in a circuit of the upper heating element when electrical power is supplied to the water heater.
 10. The controller of claim 8, wherein the upper heating element activation signal is an electrical characteristic of the water heater when electrical power is supplied to the water heater.
 11. The controller of claim 10, wherein the electrical characteristic is a current at an electrical input of the water heater.
 12. The controller of claim 10, wherein the electrical characteristic is a resistance at an electrical input of the water heater.
 13. The controller of claim 8, wherein the upper heating element activation signal is at least one sensor signal identifying whether the upper heating element, the lower heating element, or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater.
 14. A controller for controlling reheating of a tank-style water heater having at least an upper heating element and a lower heating element, wherein: the controller is adapted to selectively permit and deny supply of electrical power to the water heater; and the controller executes program logic for: identifying whether the upper heating element will be energized when electrical power is supplied to the water heater; and supplying the electrical power to the water heater only when the upper heating element will be energized thereby.
 15. The controller of claim 14, wherein the controller is adapted to detect an upper heating element activation signal indicating activation of the upper heating element.
 16. The controller of claim 15, wherein the upper heating element activation signal is a current in a circuit of the upper heating element when electrical power is supplied to the water heater.
 17. The controller of claim 15, wherein the upper heating element activation signal is an electrical characteristic of the water heater when electrical power is supplied to the water heater.
 18. The controller of claim 17, wherein the electrical characteristic is a current at an electrical input of the water heater.
 19. The controller of claim 17, wherein the electrical characteristic is a resistance at an electrical input of the water heater.
 20. The controller of claim 15, wherein the upper heating element activation signal is at least one sensor signal identifying whether the upper heating element, the lower heating element, or neither of the upper heating element and the lower heating element is energized when electrical power is supplied to the water heater. 